Tetraaquabis[3-(pyridin-4-yl)benzoato-κN]manganese(II)

In the title compound, [Mn(C12H8NO2)2(H2O)4], the Mn2+ ion lies on a twofold rotation axis and has a distorted N2O4 octahedral coordination geometry formed by four water O atoms in the equatorial plane and two apical pyridyl N atoms. A three-dimensional network is formed in the crystal structure by multiple O—H⋯O hydrogen bonds between the coordinating water molecules and the free carboxylate groups.

In the title compound, [Mn(C 12 H 8 NO 2 ) 2 (H 2 O) 4 ], the Mn 2+ ion lies on a twofold rotation axis and has a distorted N 2 O 4 octahedral coordination geometry formed by four water O atoms in the equatorial plane and two apical pyridyl N atoms. A three-dimensional network is formed in the crystal structure by multiple O-HÁ Á ÁO hydrogen bonds between the coordinating water molecules and the free carboxylate groups.
Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1994); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97. Further aggregation of the monomers (1) is formed by the multiple hydrogen-bonding between the coordinated water molecules (as donors) and the uncoordinated carboxylate groups (as acceptors) (Table 1). Hydrogen-bonding system among monomers (1) is rather complicated: each water molecule forms two O-H···O hydrogen bonds with carboxylate groups of neighbouring complex molecules, while every carboxylate group of PBC forms three hydrogen bonds.
Consequently, every monomer acts as a novel six-connected supramolecular synthon to connect with six adjacent monomers. Notably, the hydrogen-bonding models of the carboxyl group of PBC play an important role in the formation of crystal structure of (1). For example, as shown in Fig. 2, the O1 atom of the carboxylate group of PBC in a hydrogenbonding bridging mode ligates to two water molecules from two neighboring monomers, and as a result, monomers (1) are regularly arrayed in ab plane and linked into two-dimensional layers by strong hydrogen bonding (O3···O1, 2.715 (2) Å; O4···O1, 2.728 (2) Å). The layer structure is stabilized by forceful face-to-face π···π stacking interactions between adjacent benzoicate groups and pyridyl groups of PBC with a centroid to centroid distance of 3.62 (1) Å. Intriguingly, the benzoicate group and pyridyl group of PBC distort to 27.6 (0) ° to meet the formation of hydrogen bonding. The layers are further bound together to create the three-dimensional supramolecular architecture by hydrogen bonds between the O2 atom of the carboxylate group of PBC and two water molecules in the adjacent complex molecue. monomer.

Experimental
The title compound, (1), was prepared according to the following process. A mixture of MnCO 3 (0.012 g, 0.1 mmol), PBC (0.040 g, 0.2 mmol) and deionized water (10 ml) was sealed into a 25 ml Teflon-lined stainless autoclave. The autoclave was heated at 160 °C for four days. As cooled to room temperature gradually, pale yellow needle crystals of (1) suitable for X-ray analysis were obtained in 64% yield (based on Mn).

Refinement
All H atoms were located in a difference map. The coordinates of the water H atoms were refined with U(H) set to 1.2U eq (O). H atoms bonded to C were refined as riding with C-H = 0.95Å and 1.2U eq (C).

Tetraaquabis[3-(pyridin-4-yl)benzoato-κN]manganese(II)
Crystal data Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.